Police started randomly checking people for guns in the capital's 175 subway stations Saturday after a man opened fire inside a crowded station, killing two people and wounding 10.
Mexico City Attorney General Miguel Angel Mancera said the gunman, Luis Felipe Hernandez, 38, who was wounded by police, was undergoing psychological exams to determine if he is mentally unstable. Authorities have 48 hours to decide whether to send him to a psychiatric ward or have him stand trial.
Mancera said eight of those injured by Hernandez had been released from hospitals while two remained under treatment.
Hernandez was writing an anti-government statement on a wall at the packed Balderas subway station when a police officer confronted him. He fatally shot the officer and then continued firing as people got on and off a train during rush hour.
Video from a security camera shows Hernandez shooting as the crowd runs for cover.
A passenger, later identified as construction worker Esteban Cervantes, jumps out of the train and lunges at Hernandez on the platform. Cervantes continues trying to grab the gun as Hernandez fires at him. Cervantes falls back after being shot in the head.
Hernandez then walks into an open subway car, where passengers are crouched down. He steps back on to the platform to grab a bag, apparently to reload his gun, then fires repeatedly from the door.
More police officers, both in uniform and plain clothes, run onto the platform firing their guns at the shooter, who is wounded and subdued.
City police held a ceremony Saturday to honor their fallen colleague, Victor Manuel Miranda, who is survived by a common-law wife and their 1-year-old daughter.
In a poor neighborhood of cinderblock homes and gravel roads, family and friends of the construction worker slain trying to stop the shooter also held a funeral. Cervantes left behind a wife and five grown children. A rose and a photo of him smiling was placed on his wooden casket.
"I consider what he did heroic," said his son, Gerardo Cervantes. "My dad couldn't stand injustice, and I think that's why he reacted the way he did."
Attacks on public rare in city
More than 1,600 city police officers and 3,000 security guards were assigned to permanently patrol subway stations starting Saturday, using 500 hand-held metal detectors, the city government said in a news release. More than 5 million people a day use the Metro system, one of the world's busiest.
Mancera said the gunman was a farmer from western Jalisco state who after being captured rambled on about being against world politics.
"He talked about global warming and then gave a message from the Bible and all of a sudden he started focusing on some government," Mancera told the government news agency, Notimex. "The first impression he gives is that he is mentally unstable."
Mancera told Notimex that Hernandez did not test positive for drugs or alcohol. He said Hernandez had been staying at a hotel in the city since Wednesday.
The shooting shocked a city where holdups are common but such random attacks on the public are rare.
The attack came about a week after a Bolivian preacher hijacked an Aeromexico jetliner as it was landing in Mexico City after a flight from the Caribbean resort of Cancun.
The hijacker, Jose Flores, said he was acting on a divine revelation and wanted to warn President Felipe Calderon of an earthquake that would occur in 2012. That year has been widely mentioned on the Internet as the date for potentially catastrophic events, based on astronomical alignments and purported ancient prophecies.